The task that transform the primary type (info.magnolia.migration.task.content.UpdateWebsitePrimaryTypeMigrationTask) change the primary type of a STK footer area into mgnl:component instead of mgnl:area.

Why? Because the logic that return the new type is doing the following:
If the "old type" is Content, then the "new type" is page.
If the "old type" is ContentNode, then the new type is Area only if the node has no template assigned to it,otherwise it's a component.

Check here info.magnolia.migration.task.content.UpdateWebsitePrimaryTypeMigrationTask.getNewType(Node).

Footer is a special case, it an area for the 4.4 world of Magnolia but is has a template. Now in 4.5 it is still an area but its transformation must be handled differently by the migration.

Todo

Update UpdateWebsiteMainContentMigrationTask and add a special treatment for the footer.
It must be an area and the template assigned must be removed.
Do it in this method because footer is a STK specific area.

The doc must also mention that, please update the page http://wiki.magnolia-cms.com/pages/viewpage.action?pageId=56363441#MigrationprocessVersionupto12-4TransformSTK-basedwebsites